Injection molding nozzles for injection molding are known. For example hot runner injection machines feed liquefied plastic material from the bushing of an injection molding machine to an injection gate of a mold cavity to mold the desired article therein. Examples of prior U.S. Patents relating to injection molding nozzles and machines include U.S. Pat. Nos. 4,173,448; 4,588,367; 4,662,837; 4,682,945; 5,374,182; and 5,533,882, all of which are assigned to the assignee of the preset invention and the contents of all of which are incorporated herein by reference.
While injection molding and nozzle assemblies are well known, problems still exist with prior art injection nozzles. For example, leaking of liquefied plastic from various connection points within the nozzle assembly, the manifold and the injection machine is a continuing problem. In particular, such leaked material can remain within the nozzle assembly, being heated for time periods in excess of those intended within normal processes, resulting in crystallization and other deleterious effects in the material. This leaked material can contaminate ongoing injection operations and generally results in difficulty in servicing nozzle assemblies and machines. Further, some materials are corrosive or otherwise aggressive to materials within the nozzle assembly and their continued presence within the nozzle assembly due to leaking can result in decreased service lifetimes.
The problem of leaking has proven to be a difficult one to address due to the wide range of operating temperatures which can be required, depending upon the plastic material and/or injection process. As the nozzle assembly is formed of components subject to thermal expansion and contraction, and in fact such components can have different thermal expansion coefficients, generally a nozzle assembly is designed for use within a relatively narrow operating temperature window such as 20.degree. C. or, at best, 30.degree. C. about the designed operating temperature. While the materials, design and clearances within the nozzle assembly are carefully selected to reduce leaking within the operating temperature window, operation outside this operating temperature window often results in unacceptable leaking.
As will be apparent, a narrow operating temperature window limits use of the nozzle assembly to specific processes and/or configurations. To supply nozzle assemblies with different required operating windows, a supplier must maintain a wide inventory of components with different designs, dimensions and/or which are formed of different materials.
Another difficulty with prior art injection nozzles is that, with the exception of the invention disclosed in the above-mentioned U.S. Pat. No. 5,533,882, injection nozzles can only be serviced by removing the mold from the injection molding machine and then disassembling the mold to remove the nozzle assemblies from the back side of the mold.